Usually used with a return pump, this flow sensor can be placed in line with the flow on any pipe, connected to the FMM, and communicate to your Apex the flow rate of water through that pipe. The FS-200 will work with flow rates from 300-3000 gph.
Connections sold seperately -
Adaptor Socket Female 63mm x 2"
https://charterhouse-aquatics.com/shop/aquatics/fittings/female-adaptor-sockets